Visible crew/equipment: At Hoover Dam, after the salute, when Defense Secretary Keller speaks with Lennox and Epps, the reflection of the white reflector screen is visible on Keller's glasses. What's more, the boom mic's reflection is actually visible within the reflector screen's reflection. Two for the price of one. (01:35:30)
Visible crew/equipment: As Barricade and Bumblebee are fighting, when Frenzy attacks Sam and pulls off his pants, the padded black knee guard (with a white stripe at the top and bottom) that Sam wears on his right leg is visible when he is lying on his back, just after he shouts, "He's gonna kill me!" It's gone in the previous and following shots. (00:53:50)
Visible crew/equipment: When Sam is talking to Mikaela's boyfriend, you can see the camera and crew reflected in the Hummers mirrors. (00:20:20)
Visible crew/equipment: On the way to Mission City, just before Sam spots Optimus Prime, when the camera shows the front of Optimus Prime the camera truck/operator is reflected on the bumper. (01:48:20)
Visible crew/equipment: When Sam tries to hand off the All Spark, the chopper is shot down by Starscream. When the chopper wreckage flies over Sam lying on the ground, the black protective gear is visible between Sam's pants and tee shirt. (02:05:45)
Visible crew/equipment: After the fight with Scorponok, the soldiers are waiting for the smoke cloud to settle. As the camera is moving behind the soldiers, a camera shadow is moving to the bottom left of the screen. (00:44:25)
Visible crew/equipment: When Sam and his friend head for the party at the lake, as they drive by the lake and the camera cranes up to show the lake, you can blatantly see the shadow of the camera on the crane moving up. (00:20:05)
Visible crew/equipment: When Banachek and Simmons are talking to Sam at the entrance of the Hoover Dam, you can see the white lighting panels reflected in their sunglasses. (01:36:30)
Visible crew/equipment: After Glen sends the message, the soldier says, "Sir, I have authenticated air strike order from Sec Def.," In the next shot, just as Prime's silver bumper beneath the grille comes into view, the reflection of the crewmember who is standing on the filming vehicle's camera platform, beside the mounted camera, is visible on the right side. (01:49:30)
Visible crew/equipment: During the attack on Hoover Dam, after Simmons rejects Sam's request to be brought to Bumblebee, when Simmons tells Lennox to drop his weapon, in the next overhead wideshot the grey tape marker between Lennox's and Simmons's feet is visible, as well as the tape marker at Secretary Keller's feet. (01:43:15)
Visible crew/equipment: After the agents are handcuffed, when the Autobots transform into their respective vehicle modes as one of them says, "Roll out!", there are three black ramps positioned in front of the sidewalk, which were not there before. The Autobots use them when driving up onto the sidewalk. (01:24:20)
Visible crew/equipment: After Bumblebee locks its doors with Mikaela and Sam inside, the Camaro speeds past Barricade and does a 180° spin. Just before the shot cuts away, as the passenger door first opens there is a perfect view of the back right tire, where we can see the stunt cable attached to under the tire. (00:52:50)
Visible crew/equipment: When the soldiers discover the telephone line in Qatar, Scorponok tears down the tower. As the tower hits the ground we get a frontal view of the soldier wearing glasses. As the soldier turns his head we can see the film crew reflected in his glasses. (00:39:05)
Visible crew/equipment: After Banacheck walks away with Sam and Mikaela, when Agent Simmons stands by himself on the Hoover Dam intake tower walkway and says, "The man's an extortionist," the reflector screen is reflected in his sunglasses. (01:36:20)
Visible crew/equipment: When Sam falls on the sidewalk with the cube and the machines start coming alive during the fight scene in the city, a fast shot shows a cameraman with the camera on the hands on the right side of the screen. (02:02:16)
Visible crew/equipment: When Sam rushes to his waiting father after class and tells him about the A- they drive off. In the next close-up shot the filming vehicle, with its top mounted crane and camera at its front end, are reflected on the car's surface as they drive past, before pulling into the Porsche lot. As this shot continues, when they drive onto the Porsche lot, the filming vehicle directly behind them (note its headlights), is reflected on the large windows in front of them and when Sam is told he isn't really getting a Porsche the filming vehicle, which is now beside them, is reflected on the window to their left. (00:11:45)
Visible crew/equipment: After Sam is interrogated by Barricade, when Sam knocks Mikaela off her moped the black protective gear that Mikaela wears is visible. It is gone when she gets in the car with Sam. (00:51:05)
Visible crew/equipment: When the base in Qatar is attacked, in one shot two crew members, one with a camera, can be seen towards the left side of the screen. (00:06:55)
Visible crew/equipment: Upon arrival at Hoover Dam, just as Sam exits the SUV the reflection of the camera/crane is visible on the vehicle's black surface, at the left, just before it tracks backwards into an overhead shot. (01:34:25)
Visible crew/equipment: In the aerial shot, as Starscream flies past the glass building with the names "Deloitte and Touche" (before his first attack on those in Mission City), we see the reflection of the filming helicopter behind Starscream, just beneath the names. (01:53:20)
Chosen answer: There is no reason to think they can't. They simply choose not to. They may feel it's too deceitful.
Actually in this movie (when joining up with bumblebee and the others after they pick up the All Spark) and Revenge of the Fallen, Ironhide uses holographic humans in his cargo bed. Also, Arcee and the twins use holographic drivers at the beginning scene in Revenge of the Fallen.